Parent Advice - Grad School LOR Thank Yous

One of my kids asked me a question, and I have no idea what to suggest. I thought I'd post it here instead of the Grad School board because this board seems to always know the right things to do. My child is applying to grad school. His professors have been incredibly generous in writing letters of recommendation for him, and he would like to thank them appropriately. He's writing thank you letters to them, but is there a gift he should include or would the letter be enough? These professors have been cheering him on for quite some time, and one in particular is a mentor to him. I didn't go to grad school so I don't know what is appropriate outside of a letter. I saw a thread where someone said their child was baking something for their professors as a thank you. Trust me, no one wants this kid to bake anything to show appreciation, but these professors have put so much time and energy into his application process that he doesn't want to offend them by under-thanking them (if that makes sense). Thank you so much for any guidance!

My S gave the teachers who recommended him each a baseball cap with his college name on it. Whatever you decide, it shouldn't be anything big -- recommendations are a part of their job. I do think a little something (chocolates, a candle, a small plant) is nice, though!

Gift card is awkward. Just a handwritten thank you. We are an academic family and write many LORs. It gets weird if students -- undergrads or grad students -- do something more than that, because now the prof feels "indebted" for something that is part of our job so then feels obligated to reciprocate.

Just write thank you, on stationary rather than email. And keep the professor updated with acceptances.